To package an integrated circuit (IC) chip or die, such as a processing device or a memory device, the IC die is typically mounted on a substrate, this substrate often referred to as the “package substrate.” The package substrate includes a plurality of leads that are electrically coupled with the leads of the IC chip, as well as circuitry to route signals to and from the die. For a flip-chip package—employing, for example, Controlled Collapse Chip Connect (or “C4”) assembly techniques—an array of bond pads on the IC die are coupled to a corresponding array of leads, or “lands”, on the package substrate by an array of connection elements (e.g., solder balls, column, etc.). Alternatively, the IC chip bond pads may be connected to the leads on the package substrate using wirebonding or another suitable process.
The circuitry provided by the package substrate routes the IC chip leads to locations on the package substrate where electrical connections can be established with a next-level component (e.g., a motherboard, a computer system, a circuit board, another IC device, etc.). For example, the substrate circuitry may route all signal lines to a ball-grid array—or, alternatively, a pin-grid array—formed on a lower surface of the package substrate. The ball- or pin-grid array then electrically couples the packaged IC die to the next-level component, which includes a mating array of terminals (e.g., lands, pin sockets, etc.). Alternatively, the circuitry may route the signal lines to locations proximate the periphery of the package substrate, wherein wirebonding may be used to couple the packaged IC chip to the next-level component.
The IC die is typically attached to the package substrate using an epoxy or other suitable adhesive. This epoxy forms an “underfill” layer that both attaches the die to the package substrate and provides mechanical support for the die and the electrical connections (e.g., solder elements) between the IC die bond pads and the substrate's leads. To minimize voids in the underfill layer, the adhesive (or “underfill material”) is typically deposited on the package substrate in a glob or mound, wherein this glob is dispensed onto the package substrate at a location where the die will be attached. When the die is compressed against the package substrate, the underfill material flows outwardly toward the periphery of the die, such that the underfill material forms a substantially void-free and uniformly thick layer underlying the entire lower surface of the die (or a substantial portion thereof).
An example of the attachment of an IC chip to a package substrate using an underfill material is illustrated in FIGS. 1A through 1C. Referring to FIG. 1A, a package substrate 110 includes a number of leads or lands 115, the lands 115 being arranged in an array. A nozzle 105 or other dispenser (e.g., syringe, dropper, etc.) has dispensed a glob 132 of underfill material (e.g., epoxy) onto an upper surface of the package substrate 110. As shown in FIG. 1B, an IC die 120 has been positioned over the substrate 110. The IC die 120 includes a plurality of connection elements 125, wherein each connection element 125 (e.g., a solder ball, column, etc.) is connected with a bond pad (not shown in figures) on the IC die 120. The connection elements 125 on IC die 120 are arranged in an array corresponding to the arrangement of the lands 115 on the package substrate 110.
Referring now to FIG. 1C, the IC die 120 has been joined with the package substrate 110 to form an IC package 100. The die 120 has been compressed against the substrate 110, and the underfill material 132 has been forced to flow outwardly from the interior of the die 120 toward the periphery thereof to form an underfill layer 130. By placing the underfill material 132 near the center of the substrate (or near the center of the array of lands 115) and forcing this material to flow outwardly under the force of compressing the die 120 against the substrate 110, voids in the underfill layer 130 are minimized and a substantially uniform underfill layer 130 is formed. Solder reflow may then take place to electrically connect each connection element 125 to its mating lead 115 on the package substrate 110 and, if necessary, any post-curing of the underfill layer 130 may be performed. As noted above, the underfill layer 130 attaches the die 120 to the package substrate 110 and also provides mechanical support for the substrate-to-die electrical connections (e.g., leads 115, connection elements 125, and the die bond pads).
Time-pressure type dispensing systems, such as the nozzle 105 shown in FIG. 1A, have proven adequate with respect to deposition of the underfill material at the correct location and in a desired shape (i.e., a shape having a height that is greater than the thickness of the final underfill layer, such that the underfill material flows outwardly under compression of the die against the substrate). However, these time-pressure dispensers are relatively slow, and their use can negatively impact the pace of a production line.